Remove unix-2.8 patching for now

I originally patched these libraries in anticipation of GHC HEAD
bundling the yet-to-be-released `unix-2.8` instead of `unix-2.7`.
However, since then HEAD has switched back to `unix-2.7` and doesn't
show any signs of going back to `2.8` any time soon. Keeping these
patches around, therefore, is a bit wasteful since it results in
more `Cabal` store cache misses without any benefits, since these
libraries build on HEAD just fine. Until the need to actually adjust
to `unix-2.8` arises once more, I'm going to remove these patches
for now.